Effect of excess alpha-hemoglobin chains on cellular and membrane oxidation in model beta-thalassemic erythrocytes.

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Abstract
While red cells from individuals with beta thalassemias are characterized by evidence of elevated in vivo oxidation, it has not been possible to directly examine the relationship between excess alpha-hemoglobin chains and the observed oxidant damage. To investigate the oxidative effects of unpaired alpha-hemoglobin chains, purified alpha-hemoglobin chains were entrapped within normal erythrocytes. These "model" beta-thalassemic cells generated significantly (P < 0.001) greater amounts of methemoglobin and intracellular hydrogen peroxide than did control cells. This resulted in significant time-dependent decreases in the protein concentrations and reduced thiol content of spectrin and ankyrin. These abnormalities correlated with the rate of alpha-hemoglobin chain autoxidation and appearance of membrane-bound globin. In addition, alpha-hemoglobin chain loading resulted in a direct decrease (38.5%) in catalase activity. In the absence of exogenous oxidants, membrane peroxidation and vitamin E levels were unaltered. However, when challenged with an external oxidant, lipid peroxidation and vitamin E oxidation were significantly (P < 0.001) enhanced in the alpha-hemoglobin chain-loaded cells. Membrane bound heme and iron were also significantly elevated (P < 0.001) in the alpha-hemoglobin chain-loaded cells and lipid peroxidation could be partially inhibited by entrapment of an iron chelator. In contrast, chemical inhibition of cellular catalase activity enhanced the detrimental effects of entrapped alpha-hemoglobin chains. In summary, entrapment of purified alpha-hemoglobin chains within normal erythrocytes significantly enhanced cellular oxidant stress and resulted in pathological changes characteristic of thalassemic cells in vivo. This model provides a means by which the pathophysiological effects of excess alpha-hemoglobin chains can be examined.